1. Field of the Invention
The present invention is directed to the synthesis and stabilization of neutral molecules containing homonuclear single or multiple bonds, methods of preparation, and uses thereof.
2. Background Art
Molecules containing C—C multiple bonds are ubiquitous and have been studied for more than two centuries. In contrast, realization of the potential of homonuclear multiple bond chemistry of carbon's immediate neighbors boron and silicon has long frustrated chemists. For instance, it was not until 1981 that a disilene, a compound containing a Si—Si double bond (R2Si═SiR2, where R is Me3C6H2), was prepared by West et al, wherein the central Si atoms were in the formal oxidation states of two (+2). The first disilyne (RSi≡SiR, where R is an extremely bulky ligand), a compound containing a Si—Si triple bond (albeit with a decidedly nonlinear, transbent geometry), was ultimately achieved by Sekiguchi et al. in 2004. The formal oxidation state of Si atoms in Sekiguchi's disilynes was reported to be (+1).
It is well known for transition metals to assume the formal oxidation state of zero in organometallic compounds (for example, Ni(CO)4, (C6H6)2Cr, etc.). However, the formal oxidation state of zero is rare for main group elements in their compounds (apart from those in Zint1 phases). Si(0) intermediates are promising candidates for the development of new synthetic strategies in silicon chemistry. However, due to their high reactivity and instability, evaluation of Si(0) compounds requires sophisticated instruments and elaborate techniques, such as matrix isolation. The diatomic Si2 molecule, having a triplet ground state (X3Σg−), has been studied only in the gas phase and in argon matrices. For instance, the CO complex of the Si2 molecule, OC:Si═Si:CO, was examined with argon matrix isolation absorption infrared spectroscopy and computed to have an unusual transbent structure with Si—Si—C angles approaching 90°. However, stabilization of the fleeting diatomic Si2 molecule has never been achieved.
Similarly, no one previously has been able to produce a stable neutral molecule containing a B═B bond. The diboron dianions [R2BBR2]2− (I), and their alkali metal salts, were proposed as promising B═B double bond candidates two decades ago. However, corroborating synthetic and structural evidence has been rare. Similarly, the highly reactive parent neutral diborene, HB═BH (II), has only been characterized in matrices.

The electron deficiency of boron in (II) lead to theoretical work on its complexation with appropriate Lewis base ligands as a promising approach to viable L(H)B═B(H)L derivatives. Computational prediction of the carbonyl-stabilized diborene, OC(H)B═B(H)CO, was made based on the theoretical development of BCO chemistry. However, such complexes have not been experimentally realized.
The allotropy of phosphorus—white, red, and black—is well documented. Normally, phosphorus prefers a tetrahedral form P4 because P—P pi-bonds are high in energy. Pyrolysis of white phosphorus, P4, yields the high temperature diphosphorus allotrope, gaseous P2. Diphosphorus is very reactive with a bond dissociation energy half that of its ubiquitous lighter congener dinitrogen. The highly reactive and association-prone nature of P2 compared to the legendary inert nature of N2 also raises a question of a possibility to stabilize the P2 molecule.
Generally, diphosphorus functions as four-, six-, and eight-electron donor ligands in transition metal carbonyl complexes. For instance, Cummins and co-workers reported the “mild thermal extrusion” of P2 from niobium diphosphaazide complexes and that the Pt(0) species, (C2H4)Pt(PPh3)2, can serve as a trap for W(CO)5-complexed P2 molecules. In all these examples, P2 behaves as a typical Lewis base by donating its electron pair to the ligand. To our knowledge, no one has been able to synthesize, isolate, and characterize a stable molecule with a P2 nucleus, wherein phosphorous serves as an electron pair acceptor and, thus, mimics the behavior of a Lewis acid.
We now demonstrate stabilization of highly unstable homonuclear species Si2, B2H2, and P2 with persistent carbene ligands.